GRADE OF STABILITY IN FUZZY CHATTER STABILITY LOBE MODEL IN MILLING

The machining productivity and part quality are typically limited by the regenerative chatter induced by the dynamic interactions of spindle-holder-tool combination system. The conventional chatter stability model predicts the permissible stable axial depth of cut versus spindle speed by plotting the stability lobe diagram which represents two independent regions as absolutely stable zone and instable zone divided by the critical lobe curve. In fact, it is more reasonable to be a transition stage between the stable and instable zone. This paper introduced the grade of stability (GOS) to improve the conventional chatter stability model and study the transition zone in the stability lobe diagram. The variation of transition zone width with the stability sensibilities for different order lobe curve in milling system was analyzed. Sigmoid function was used as the membership function to develop the fuzzy stability lobe model. Then, the fuzzy stability lobe diagram with an adjustable slope coefficient was implemented to improve the mould steel milling process. The improved fuzzy stability model enhances the reliability of stability lobe diagram and guarantees the chatter-free milling process.     

RECONSTRUCTION OF LAYER DATA WITH DEFORMABLE B-SPLINES

0 INTRODUCTIONReverse engineering is a technology to establish CAD mod-els from samples, prototype, molds or manufacturing parts bydigitization. In many research and application areas such asmedical science, biomedical engineering, and CAD/CAM, anobject i…     

SIMULATION OF THE PROCESS STABILITY OF HPC MILLING OPERATIONS

The optimisation of high-performance cutting (HPC) processes under technological and economical aspects often proves to be extremely difficult due to the appearance of process instabilities, so-called “chatter”. The identification of ideal process parameters often involves the systematic testing with varied cutting parameters. Simulation of the process stability offers a less costly way of optimising processes prior to production. However, the predictions for the stability of high performance milling processes exhibit great deviation from experimental results. The objective is to analyse and to prevent errors within the simulation methods to make stability simulation a reliable tool in process planning. In order to improve the quality of stability simulation, the interacting Systems “Machine Tool” and “Cutting Process” are analysed individually. Methods for the coupled simulation of both systems are implemented to identify stable working conditions. As a result of this work, a time domain simulation environment for the investigation of high performance milling operations is presented. It considers the complex behaviour of the cutting process as well as the speed dependent machine tool dynamics. Cutting tests have been conducted to verify the benefit of the enhanced simulation method.     

PROBABILISTIC PREDICTION OF BURR PATTERNS OF 1045 CARBON STEEL IN FACE MILLING

Face milling burrs in ductile materials such as 1045 carbon steel exhibit three distinct burr patterns: uniform, wavy, and secondary burrs. It is found that the three burr patterns are dependent on the in-plane exit angle, undeformed chip ratio, and undeformed chip area at the exit stage of cut. Empirical equations, representing the burr transition curves from the uniform to wavy burr and wavy to secondary burr, are found. Based on the empirical relationships, a probabilistic model, in which the operational Bayesian modeling approach is adopted to include the empirical equations, is derived for burr prediction.     

难加工材料型腔圆角数控铣削的切削力预测

在难加工材料型腔的数控铣削过程中,圆角区域的加工阶段,径向切削深度和真实进给量的变化很大程度上影响切削力,造成扎刀、撞刀、振动等很多的问题, 影响工件的加工准确度和刀具的寿命,甚至使得加工无法顺利进行.文中建立端铣刀和圆角轮廓几何关系的数学模型,提出普遍适用于矩形与梯形型腔圆角的切削力预测方法.最后,对型腔圆角切削力的变化规律预测方法进行验证.     

SUPPRESSION OF PERIOD DOUBLING CHATTER IN HIGH-SPEED MILLING BY SPINDLE SPEED VARIATION

Spindle speed variation is a well known technique to suppress regenerative machine tool vibrations, but it is usually considered to be effective only for low spindle speeds. In the current paper, spindle speed variation is applied to the high speed milling process, at the spindle speeds where the constant speed cutting results in period doubling chatter. The stability analysis of triangular and sinusoidal shape variations is made numerically with the semi-discretization method. It is shown that the milling process can be stabilized by increasing the amplitude of the spindle speed variation, while the frequency of the variation has no significant effect on the dynamic behaviour. The results are validated by experiments. Based on the analysis of the machined workpieces, it is shown that the surface roughness can also be decreased by the spindle speed variation technique.     

CORRELATION-BASED ESTIMATION OF CUTTING FORCE COEFFICIENTS FOR BALL-END MILLING

This article presents a methodology to estimate cutting force coefficients based on the least squares approximation using correlation factor between the estimated and measured cutting forces in order to determine the corresponding tool angular position. This method can be applied on measured cutting force data over any small interval of time that need not contain information of the time instant when the cutting tool enters the workpiece, which has been the main requirement in the conventional method. This allows a quick estimation of the cutting force coefficients regardless of the chosen cutting conditions and tool-workpiece material, which is often the case in industrial machining processes. This proposed method has been validated by comparison of cutting force coefficients obtained using conventional estimation technique for a slot ball-end milling test. Besides being useful for predictive evaluation of forces, such estimation of cutting force coefficients of the cutting force model can be useful for understanding variations in cutting process over the tool life and can assist in online monitoring and process optimization.     

AN ANALYTICAL MODEL OF OBLIQUE CUTTING WITH APPLICATION TO END MILLING

A new analytical cutting force model is presented for oblique cutting. Orthogonal cutting theory based on unequal division shear zone is extended to oblique cutting using equivalent plane approach. The equivalent plane angle is defined to determine the orientation of the equivalent plane. The governing equations of chip flow through the primary shear zone are established by introducing a piecewise power law distribution assumption of shear strain rate. The flow stress is calculated from Johnson-cook material constitutive equation. The predictions were compared with test data from the available literature and showed good correlation. The proposed model of oblique cutting was applied to predict the cutting forces in end milling. The helical flutes are decomposed into a set of differential oblique cutting edges. To every engaged tooth element, the differential cutting forces are obtained from oblique cutting process. Experiments on machining AISI 1045 steel under different cutting conditions were conducted to validate the proposed model. It shows that the predicted cutting forces agree with the measurements both in trends and values.     

FUZZY EXPERT SYSTEM FOR PREDICTION OF KERF QUALITIES IN PULSED LASER CUTTING OF TITANIUM ALLOY SHEET

Laser cutting is an advanced thermal cutting process of complex nature. It's process behavior drastically changes with slight variation in processing conditions. The prediction of process performance becomes more difficult if cutting materials have non-favorable optical and thermal properties. Titanium (Ti) alloys are characterized by their low thermal conductivity and high chemical reactivity at elevated temperature and hence difficult to cut by laser. It has been found that complex and nonlinear behavior of manufacturing process can better be dealt with the application of artificial intelligence (AI) tools. The aim of present research is to develop a fuzzy expert system for prediction of the laser cutting process behavior of Ti alloy (Ti-6Al-4 V) sheet. A hybrid approach of neural network and fuzzy logic theory has been applied to develop the fuzzy expert system to predict the kerf widths and kerf deviation. The predicted results have been compared with the experimental data and found appropriate. The effects of significant process parameters on the different quality characteristics such as kerf widths and kerf deviation have been discussed.     

HIGH SPEED MILLING OF GRAPHITE ELECTRODE WITH ENDMILL OF SMALL DIAMETER

Graphite becomes the prevailing electrode material in electrical discharging machining (EDM)currently.Orthogonal cutting experiments are carried out to study the characteristics of graph- ite chip formation process.High speed milling experiments are conducted to study tool wear and cutting forces.The results show that depth of cut has great influence on graphite chip formation.The removal process of graphite in high speed milling is the mutual result of cutting and grinding process. Graphite is prone to cause severe abrasion wear to coated carbide endmills due to its high abrasive- ness nature.The major patterns of tool wear are flank wear,rake wear,micro-chipping and breakage. Cutting forces can be reduced by adoption of higher cutting speed,moderate feed per tooth,smaller radial and axial depths of cut,and up cutting.     

基于超分辨率重建的亚像素图像配准

针对低分辨率图像在配准过程中精度较低的问题,提出了一种基于超分辨率重建的亚像素图像配准方法。首先,对具有1至9像素位移的图像序列进行10倍降采样,获取具有0.1至0.9亚像素位移的图像序列。然后,根据图像的获取过程建立数学模型,以Bayes理论为基础,使用最大后验概率法(MAP)对亚像素位移低分辨率图像进行超分辨率重建,获取高分辨率图像。最后,使用具有亚像素配准精度的扩展相位相关法对图像进行配准。配准实验与噪声实验表明,所提方法的最大配准误差为0.03pixel,能实现对低分辨率图像的亚像素级配准,具有配准精度高、噪声抗干扰能力强等特点,可同时满足可见光图像与红外图像的高精度配准要求。     

基于相空间重构的驾驶风格定量评估

驾驶风格评价是智能交通领域的重要研究课题,一般采用频域或时域的分析方法对其进行定性的分类和识别,缺乏客观定量的评价体系。提出一种基于相空间重构的驾驶风格定量分析方法。首先,采用汽车测试数据和局部性神经网络建立个性化的驾驶员模型;然后,将个性化驾驶员模型应用于标准驾驶周期测试工况的速度跟随试验,以实现驾驶行为的标准化;最后,对标准化驾驶行为进行相空间重构,提出一种基于关联维数的驾驶风格指数,用于定量评估驾驶的激进程度,并应用于驾驶员风格的识别,仿真结果验证了所提方法的有效性。     

SURFACE INTEGRITY OF HIGH-SPEED FACE MILLED Ti-6Al-4V ALLOY WITH PCD TOOLS

This study is focused on the machined surface integrity of Ti-6Al-4V alloy using polycrystalline diamond (PCD) tools under wet milling condition. The surface integrity in terms of surface roughness, surface topography, microhardness, microstructure, and metallurgical alternations is investigated. The observations and conclusions are primarily focused on the effect of cutting speed (250–2,000 m/min) on the surface and subsurface of the machined Ti-6Al-4V. Experimental results show that machined surface integrity of Ti-6Al-4V alloy is sensitive to the variation of cutting speeds. Obvious machining (feed) marks can be found on the machined surfaces. Micro hardness examinations showed 5–20% hardening of the top machined surfaces than the bulk material. The analyses of microstructure and metallurgical alternations reveal that slight subsurface microstructure alteration such as plastic deformation on the subsurface and no phase transformation were observed. The evolution of crystallographic texture induced by the intense plastic deformation of the machined surface should be responsible for the modifications of the peak intensity radios in XRD patterns as well as higher peak broadening crystal structures.     

相对关联距离熵在转子系统故障诊断中的应用

将相对关联距离熵应用于航空发动机转子-机匣系统状态识别和故障诊断。在相空间重构的基础上，基于实测的航空发动机机匣振动时间序列求解了转子-机匣系统不同工作状态和故障状态的相对关联距离熵，并基于相对关联距离熵，对航空发动机转子-机匣系统进行了状态识别和故障诊断。     

基于混沌理论的平板闸门流激振动特性

鉴于闸门流激振动过程的复杂性,对水弹性模型试验中闸门在不同开度下的实测加速度响应数据进行了混沌特性分析。首先,对实测数据进行相空间重构,分别采用平均互信息法和平均伪最近邻域法计算最佳时间延迟和最佳嵌入维数;然后,基于嵌入参数计算关联维数D_2和最大Lyapunov指数λ_1,并对各计算参数的分布规律进行分析。研究表明:闸门侧向振动的复杂性相对其他振动方向更高,中间开度时的振动复杂性比大开度或小开度更显著;竖直向振动与顺流向振动中呈现出了较低维(D_2=3.342~5.130)的混沌吸引子,表明较少的独立变量即可描述闸门竖直向及顺流向振动的规律;λ_1随闸门开度的变化规律呈现"两边小中间大"的趋势,表明闸门在中间开度时的振动预测准确性较低。     

基于相空间重构的制造系统混沌研究

针对制造企业的生产效率时间序列体现的非线性的确定而又类似随机的特点,提出了基于相空间重构的制造系统的混沌研究方法。利用互信息法和CAO氏方法分别确定最佳延迟时间和最小嵌入维数,利用生产效率时间序列对制造系统相空间重构,通过Grassberger-Procac-cia算法和小数据量方法计算关联维数和最大Lyapunov指数这两个非线性特征量,结果表明制造企业在运行过程中出现混沌现象。     

基于变换域Hough变换的遥感图像相干干扰分析

相干干扰的存在严重地影响了对遥感图像中目标的特征提取和识别的精度,降低了各种遥感定量分析方法的有效性。通过对相干干扰的幅度和相位特性的定量分析,本文提出了相干干扰的小视场模型和大视场模型,并给出了基于变换域的Hough变换算法。实践表明,与传统的邻域平均、中值滤波、经典频域滤波等消除干扰算法相比,该算法不仅高质量地消除了遥感图像中的相干干扰,同时还能有效地保留原图像中的细微影纹和边缘信息,并获得较好的峰值信噪比。该方法已在航天遥感图像的实时采集及处理系统中获得成功应用。